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R. G. Wilson and D. E. Petzold

Abstract

A mathematical model is presented which is used to calculate the flux of solar radiation to a melting snowpack in sub-arctic woodlands. Using tree height, branch radius, and distance between trees as input data, the model calculates both hemispherical and angular view factors. The latter are checked by a special photographic technique and good agreement is obtained. The view factors are used in conjunction with measurements of global and diffuse solar radiation at a base station to calculate the corresponding fluxes in nearby woodland. A test of the model at Schefferville, Quebec, showed that calculated and observed values were highly correlated, although the model consistently produced slight underestimates.

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V. G. Koutitonsky and R. E. Wilson

Abstract

A numerical model which solves the linearized, quasi-geostrophic potential vorticity equation is used to describe free subinertial coastal-trapped wave (CTW) properties in channels with variable depth in the offshore direction, and with surface intensified buoyancy frequency profiles N 2(z) as found in large and deep estuaries. The variational form of the pressure equation reveals that CTWs propagate slower in channels as compared to those on continental shelves, due to the bottom slope reversal between the channel shores. Significant phase speed reduction occurs when the effective channel stratification parameter in O(1) or higher. Without coastal walls, phase speeds of long topographic waves increase with channel width and vertical averaged N 2, but decrease with channel concavity and N 2 surface intensification. Bottom-trapped motion is enhanced in channels relative to that on continental shelves, again due the bottom slope reversal. In the presence of coastal walls, hybrid waves are less affected by the midchannel bottom slope reversal. No “kissing”phenomenon is detected in the dispersion relations for channels with surface or subsurface (two-layer) N 2 intensification.

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Richard G. Wilson and Wayne R. Rouse

Abstract

Energy balance measurements of evapotranspiration from a developing corn crop are compared with daily equilibrium evapotranspiration estimates to examine the accuracy of the model and the environmental conditions under which it can be applied. Equilibrium estimates compared closely (a standard error of 6%) with the measured values when the surface was moderately dry, a condition which applied to 14 of the 24 days of the experiment. The ratio of actual evapotranspiration to available energy and the Bowen ratio are used to establish moisture and temperature limits for the model. The success of the model was related to a typical diurnal pattern of the difference between actual and equilibrium evapotranspiration which reflects expected variations of moisture stress during daytime hours. The performance of the model was nearly independent of the physical condition of the surface and the height of the required air temperature measurement. An equation is presented which permits easy calculation of equilibrium evapotranspiration from air temperature, net radiation, and soil heat flux data.

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G. Szeicz, D. E. Petzold, and R. G. Wilson

Abstract

No abstract available.

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G. Szeicz, D. E. Petzold, and R. G. Wilson

Abstract

In the subarctic region of central Labrador wind speeds were measured at 2 m height in open lichen woodlands of various stand densities and were related to standard winds recorded at the same level on the local airport site. The resulting reduction in wind speeds are shown to be closely related to stand parameter h * which is a function of average tree height, stand density and shrub cover; variables that can easily be obtained from airphotos or from direct ground surveys. The equation giving the ratio of wind in the woodland u(s)to that measured at the air field u(s) is u(s)=u(s)(1+βh *)−2 with β=1.16 for s=2, and s=2.0 m. The equation seems applicable to various types of stands that do not streamline in wind, ranging from open lichen cover without trees, to a dense but leafless deciduous winter hardwood forest stand. For the typical and geographically widespread open lichen woodland of the subarctic, h * was related to the usual silvicultural measure of trunk diameter at breast height (DBH) offering a useful short cut in possible ground surveys.

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R. D. Hill, R. G. Rinker, and H. Dale Wilson

Abstract

The production Of nitrogen oxides (NO and NO2) by lightning flashes has been computed from a model of gaseous molecular reactions occurring as heated lightning-channel air cools by mixing with surrounding ambient air. The effect of ozone (O3) on the production of nitrogen oxides has also been investigated in this model and it has been found that the O3 oxidizes NO to NO2 mainly at the end of the cooling process. The maximum total global production rate of nitrogen oxides by lightning is estimated to be ∼6×1027 molecules per second, or 14.4×106 tonnes of NO2, per year.

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Phillip King, Lan R. McKinnon, John G. Mathieson, and Ivan R. Wilson

Abstract

The solar infrared spectra of Murcray et al. (1969) do not contain direct evidence for the presence of N2O5 in the stratosphere. Comparison of atmospheric and laboratory spectra indicate that the upper limit to stratospheric N2O5 number density is about 2 × 108 cm−3.

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F. Ravetta, G. Ancellet, J. Kowol-Santen, R. Wilson, and D. Nedeljkovic

Abstract

In March 1995 a tropopause fold was observed at the Observatoire de Haute Provence (44°N, 6°E) using simultaneous high-resolution measurements of ozone, temperature, and wind. This unique dataset was provided by an ozone lidar, a temperature lidar, and a wind field radar. These data are described and related to the meteorological context. Comparisons with mesoscale modeling of this episode are conducted to answer the question of whether there is any spatial or temporal shift between the model outputs and the observations. Temperature comparison shows a very good agreement between the modeled and the measured static stability, discarding the hypothesis of any vertical shift. Comparison of the measured and modeled meridional components of the wind insures that the model reproduces the horizontal structure of the front and its temporal evolution. To check further the model’s ability to reproduce mesoscale structures of the flow, the relationship between ozone and potential vorticity is investigated. First, a significant association is found between potential vorticity and ozone. Their distributions are in phase and the fold can be equally defined using ozone or potential vorticity. However, second-order differences are found in the vicinity of the jet streak where turbulent mixing entrains tropospheric air within the lowermost stratosphere. Second, ozone and potential vorticity ratios, which are calculated for the different air masses in the front, compare well with climatological ratio values. This is in good agreement with the well-known view of tropopause folding as an isentropic deformation of a zone of strong ozone and potential vorticity gradients. Third, this dataset is used to model the relationship between ozone and potential vorticity, which gives an easy way to switch from one field to the other.

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Rita D. Roberts, Amanda R. S. Anderson, Eric Nelson, Barbara G. Brown, James W. Wilson, Matthew Pocernich, and Thomas Saxen

Abstract

A forecaster-interactive capability was added to an automated convective storm nowcasting system [Auto-Nowcaster (ANC)] to allow forecasters to enhance the performance of 1-h nowcasts of convective storm initiation and evolution produced every 6 min. This Forecaster-Over-The-Loop (FOTL-ANC) system was tested at the National Weather Service Fort Worth–Dallas, Texas, Weather Forecast Office during daily operations from 2005 to 2010. The forecaster’s role was to enter the locations of surface convergence boundaries into the ANC prior to dissemination of nowcasts to the Center Weather Service Unit. Verification of the FOTL-ANC versus ANC (no human) nowcasts was conducted on the convective scale. Categorical verification scores were computed for 30 subdomains within the forecast domain. Special focus was placed on subdomains that included convergence boundaries for evaluation of forecaster involvement and impact on the FOTL-ANC nowcasts. The probability of detection of convective storms increased by 20%–60% with little to no change observed in the false-alarm ratios. Bias values increased from 0.8–1.0 to 1.0–3.0 with human involvement. The accuracy of storm nowcasts notably improved with forecaster involvement; critical success index (CSI) values increased from 0.15–0.25 (ANC) to 0.2–0.4 (FOTL-ANC). Over short time periods, CSI values as large as 0.6 were also observed. This study demonstrated definitively that forecaster involvement led to positive improvement in the nowcasts in most cases while causing no degradation in other cases; a few exceptions are noted. Results show that forecasters can play an important role in the production of rapidly updated, convective storm nowcasts for end users.

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F. R. Robertson, G. S. Wilson, H. J. Christian Jr., S. J. Goodman, G. H. Fichtl, and W. W. Vaughan

The present lack of a lower atmosphere research satellite program for the 1980s has prompted consideration of the Space Shuttle/Spacelab system as a means of flying sensor complements geared toward specific research problems, as well as continued instrument development. Three specific examples of possible science questions related to precipitation are discussed: 1) spatial structure of mesoscale cloud and precipitation systems, 2) lightning and storm development, and 3) cyclone intensification over oceanic regions. Examples of space sensors available to provide measurements needed in addressing these questions are also presented. Distinctive aspects of low-earth orbit experiments would be high resolution, multispectral sensing of atmospheric phenomena by complements of instruments, and more efficient sensor development through reflights of specific hardware packages.

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